Publication Date:
2021-03-29
Description:
Groundwater from the La Paz arid coastal
aquifer in Baja California, Mexico, is essentially the only
source of drinking water for the local population and
tourists, as well as irrigation water for agricultural needs.
The intensive exploitation of the aquifer and water cycling
has resulted in groundwater abatement (up to 10 m) and
high salinity (up to *5800 mg l-1). A study using
hydrochemistry, isotopic (deuterium, oxygen-18 and carbon-
14) and gaseous tracers (chlorofluorocarbons CFC-11,
CFC-12, CFC-113), as well as multivariate statistics, was
developed to elucidate groundwater composition, flow and
occurrence. Groundwater is of meteoric origin, and a large
proportion is subject to evaporation. The primary natural
recharge is generated in the El Novillo and Las Cruces
ranges, and groundwater subsequently flows in a SE–NW
direction toward the coast. The initial water type is the
result of discordant dissolution of silicate minerals and ion
exchange on soils. In the lower plain portion, the aquifer
system is recharged from irrigation return flow and seawater
intrusion, which significantly affects groundwater
chemistry. Nitrate and chloride concentrations indicate that
groundwater is highly affected by an overuse of fertilizers
in agricultural activities, but there is little effect from urban
activities. Seawater intrusion has progressed rapidly during
the past decade, and the impact currently extends 13 km
inland. Radiocarbon residence time calculations suggest
that groundwater is modern, with the exception of Chametla
and El Centerario sites in the central and western
lowlands with ages of up to *5000 years. These waters
indicate an additional recharge source for the upconing of
fossil groundwater or regional flow.
Keywords:
Coastal aquifers; Hydrogeochemistry; Arid regions; Isotope hydrology; Contamination
;
551
Language:
English
Type:
article
,
publishedVersion
Permalink
